Basic scatter plots

The plot can be created using data from either numeric vectors or a data frame:

# Use data from numeric vectors
x <- 1:10; y = x*x
# Basic plot
qplot(x,y)
# Add line
qplot(x, y, geom=c("point", "line"))
# Use data from a data frame
qplot(mpg, wt, data=mtcars)

Scatter plots with smoothed line

The option smooth is used to add a smoothed line with its standard error:

# Smoothing
qplot(mpg, wt, data = mtcars, geom = c("point", "smooth"))

To draw a regression line, read the following article: ggplot2 scatter plot

Smoothed line by groups

The argument color is used to tell R that we want to color the points by groups:

# Linear fits by group
qplot(mpg, wt, data = mtcars, color = factor(cyl),
      geom=c("point", "smooth"))

Change scatter plot colors

Points can be colored according to the values of a continuous or a discrete variable. The argument colour is used.

# Change the color by a continuous numeric variable
qplot(mpg, wt, data = mtcars, colour = cyl)
# Change the color by groups (factor)
df <- mtcars
df[,'cyl'] <- as.factor(df[,'cyl'])
qplot(mpg, wt, data = df, colour = cyl)
# Add lines
qplot(mpg, wt, data = df, colour = cyl,
      geom=c("point", "line"))

qplot(mpg, wt, data=df, colour= factor(cyl))

Change the shape and the size of points

Like color, the shape and the size of points can be controlled by a continuous or discrete variable.

# Change the size of points according to 
  # the values of a continuous variable
qplot(mpg, wt, data = mtcars, size = mpg)
# Change point shapes by groups
qplot(mpg, wt, data = mtcars, shape = factor(cyl))

Scatter plot with texts

The argument label is used to specify the texts to be used for each points:

qplot(mpg, wt, data = mtcars, label = rownames(mtcars), 
      geom=c("point", "text"),
      hjust=0, vjust=0)

Generate some data

The R code below generates some data containing the weights by sex (M for male; F for female):

set.seed(1234)
mydata = data.frame(
        sex = factor(rep(c("F", "M"), each=200)),
        weight = c(rnorm(200, 55), rnorm(200, 58)))
head(mydata)

##   sex   weight
## 1   F 53.79293
## 2   F 55.27743
## 3   F 56.08444
## 4   F 52.65430
## 5   F 55.42912
## 6   F 55.50606

Histogram plot

# Basic histogram
qplot(weight, data = mydata, geom = "histogram")
# Change histogram fill color by group (sex)
qplot(weight, data = mydata, geom = "histogram",
    fill = sex)

Density plot

# Basic density plot
qplot(weight, data = mydata, geom = "density")
# Change density plot line color by group (sex)
# change line type
qplot(weight, data = mydata, geom = "density",
    color = sex, linetype = sex)